1. Field of the Invention
The present invention relates to a traveling steel pipe cutting machine of a milling type, which cuts a pipe with rotating milling cutters.
2. Description of the Prior Art
A machine for cutting steel pipes was proposed in Japanese Patent Publication No. 62-27926 (1987) entitled "Steel Pipe Cutting Machine Provided With Revolving Type Milling Cutter", and a method therefor was proposed in Japanese Patent Publication No. 62-74525 (1986) entitled "Control Method For Cutting Of Pipes".
In the prior art, as shown in FIGS. 7 and 8, a plurality of cutter heads 2 each equipped with a milling cutter 1 rotating in the up-cut direction are supported by a revolving ring via rotary shafts 3.
This revolving ring (ring gear 10) is revolved about a center axis of a pipe 4 to be cut by the intermediary of a motor 5, gears 6 and 7, a worm gear 8, and a worm wheel 9.
Each cutter head 2 is able to swing as indicated by arcs .THETA..sub.1 and .THETA..sub.2 for the purpose of keeping a constant depth of cut. A truck on which the cutting machine is loaded can be synchronized with a line speed of the pipe 4. When the truck has been accelerated up to the synchronized speed, the pipe 4 to be cut is clamped by a clamping device (not shown) and the pipe 4 is cut simultaneously by the plurality of milling cutters 1 undergoing the above-mentioned revolution and swinging motions.
As a method of controlling the cutting, an outer diameter of the pipe 4 to be cut, a pipe wall thickness and a maximum depth of cut are preliminarily input to a computer. And, by jointly controlling the rotational position and speed and the swinging position and speed of the milling cutter 1, cutting is effected while maintaining a maximum depth of cut and a constant projection of the milling cutter 1 from the pipe wall thickness.
The prior art for cutting a steel pipe relies on effecting a revolution and swinging motions of the milling cutters. Hence, loci of the milling cutters are calculated as represented by polar coordinates. Therefore, even in the case of a square pipe having a simple configuration, the calculation and control of the desired position loci are complicated procedures.
Moreover, since the cutting machine in the prior art employs a structure in which a reaction force of the milling cutter 1 is received only by the rotary shafts 3, it has poor rigidity, and an inertial mass can be hardly chosen large. Also, as the cutting is conducted intermittently, vibrations of the cutter head 2 become large, a chip thickness cannot be made large, and the life of each cutter edge is short.
Still further, due to the fact that a plurality of cutter heads 2 are revolved in synchronism by means of a revolving ring (ring gear 10), it is impossible to cut a pipe having an asymmetric cross-sectional shape under the same operating conditions.